Microelectromechanical systems (MEMS) technology has achieved wide popularity in recent years, as it provides a way to make very small mechanical structures and integrate these structures with electrical devices on a single substrate using conventional batch semiconductor processing techniques. One common application of MEMS is the design and manufacture of sensor devices. MEMS sensors are widely used in applications such as automotive, inertial guidance systems, household appliances, game devices, protection systems for a variety of devices, and many other industrial, scientific, and engineering systems.
One example of a MEMS sensor is a MEMS accelerometer. MEMS accelerometers are sensitive to acceleration or acceleration forces. These forces may be static, like the constant force of gravity, or they can be dynamic, caused by moving or vibrating the sensor. Accelerometers may sense acceleration forces along one, two, or three axes or directions. From this information, the movement or orientation of the device in which the accelerometer is installed can be ascertained.
Commonly, MEMS accelerometers react to acceleration with a change in electrical capacitance, which causes the output of an energized circuit, connected to the sensor, to vary. One common form of MEMS accelerometer uses one or more movable structures that move under acceleration above a substrate. The movement of the movable structure changes capacitance, and the electrical circuit connected to the MEMS accelerometer structure measures the change in capacitance to determine the acceleration forces. Such MEMS accelerometers are widely used in a variety of sensing applications. For example, vehicle or automotive applications may use MEMS accelerometers to determine when to deploy the vehicle airbag or activate a stability and/or traction control system. In addition, consumer electronics devices, such as video game controllers, personal media players, cell phones, and digital cameras, also use MEMS accelerometers in various applications to detect the orientation and/or respond to movement of the device.
Traditionally, in order to sense motion along multiple axes, accelerometers have been provided that include multiple sense masses that move independently of one another in response to accelerations. As these devices continue to shrink in size, it becomes desirable to reduce the collective size of these sense masses. But reducing the collective size of the sense masses can make it increasingly difficult to provide desired sensitivity and reliability. In addition, due to smaller sizes and travel distances of the sense masses, some MEMS accelerometers are vulnerable to high impact loads.